The invention relates to a process for rapid oxidation of sulfides in aqueous solution in the presence of a certain manganese-containing catalyst. The invention further provides a process for reducing the level of hydrogen sulfide in gases by contacting said hydrogen sulfide-containing gases with a certain manganese catalyst-containing sorbent.
Many modern industrial processes employed in the paper, natural gas, coal-mining, chemical and petroleum refining industries result in production of gases and aqueous waste streams containing varying amounts of hydrogen sulfide and/or sulfide ions. The sulfide ions may be associated with any of various cations such as sodium, ammonium and the like. Concern for the environment and applicable regulations preclude the discharge of such sulfide-containing water to receiving bodies of water such as rivers, lakes, estuaries and the like.
For waste water streams containing relatively large amounts of sulfide, e.g., more than about 0.2 percent by weight, it is conventional to contact the sulfide bearing water with acid and large amounts of steam to drive off, e.g., hydrogen sulfide gas. The hydrogen sulfide gas is recovered and converted, inter alia, to elemental sulfur having utility in fertilizer and other applications. With increasing energy costs, the expense of generating the copious steam needed to implement this procedure can be very costly. Such expense is exacerbated when only small or trace amounts of sulfide are present in relatively large streams, but nevertheless large amounts of steam must be used to remove the sulfide that is present.
For waste streams that contain only trace amounts of sulfide it is known to contact the stream with a source of oxygen such as air to convert the sulfide to environmentally acceptable conversion products such as sulfate ion, and thiosulfate ion (which thiosulfate is readily biologically converted to sulfate ion). However, the rate of sulfide oxidation is very slow, and this process can require considerable capital expense for facilities to treat large waste streams and those containing sulfides significantly above trace levels.
The rate of sulfide oxidation in aqueous streams can be improved by the use of catalysts. A number of catalysts for air oxidation of sulfides are known, including some containing manganese. See, e.g., A. T. Kuhn et al. "A Review of the Air Oxidation of Aqueous Sulfide Solutions," J. Chem. Tech. Biotechnol., 33A, pp. 406-414, 1983, and M. A. Kessick et al. "Reactions Between Manganese Dioxide and Aqueous Sulfide," Environmental Letters, 7(2), pp. 163-173, 1974. However, in many instances the reaction rates still leave much to be desired.
A new process has now been discovered employing certain highly reactive catalyst and which can rapidly reduce the sulfide content of such aqueous solutions. The catalyst-containing solution can further be used to sorb hydrogen sulfide from gases in a gas-liquid contacting zone after which the solution can be passed to a further reaction zone to contact with molecular oxygen resulting in oxidation of the sulfide whereby the catalytic solution is regenerated and can then be recycled to the gas-liquid contacting zone to sorb hydrogen sulfide from further fresh sulfide containing gas.